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Microbiology in Orthopaedics

Microbiology in Orthopaedics. Elizabeth Darley Consultant Medical Microbiologist North Bristol NHS Trust. What microbiology should you know?. What are commonly implicated bacteria (Common orthopaedic infections) Prosthetic Joint Infection Diagnosis Treatment & outcome

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Microbiology in Orthopaedics

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  1. Microbiology in Orthopaedics Elizabeth Darley Consultant Medical Microbiologist North Bristol NHS Trust

  2. What microbiology should you know? • What are commonly implicated bacteria • (Common orthopaedic infections) • Prosthetic Joint Infection • Diagnosis • Treatment & outcome • Preventing post-operative infection

  3. Classification of bacteria • Basic • Gram staining (positive or negative) • Shape (rod, coccus, spiral) • Respiration (aerobic, anaerobic) • More precise • Biochemical or genetic tests • Genus • Species

  4. Microbiology of Bone and Joint infection – virulence of pathogens Increasing virulence  Potential pathogens – in receptive environment. Eg gut flora, streptococci, coliform, Often cause disease if given chance by some gap in body defences Avirulent organisms – weak pathogens eg skin floraRarely cause disease unless body defences damaged or prosthetic material in situ Causes disease in most/all cases when acquired by suitable host species Coagulase negative staphylococci, diphtheroids Bacillus anthracis Staphylococcus aureus, E coli

  5. Microbiology of Bone and Joint infection- Biofilm formation • Many/most implant infection now believed to involve biofilm • Complex communities of surface-associated cells in an extra cellular matrix. • Lack of metabolic substrates cause bacteria to enter a stationary phase, resistant to growth-dependant antibacterials eg penicillins • Physical protection from antibiotics, bacteria function en masse as a multicellular organism – can survive adverse environments • Biofilm cells change their phenotype (may be less susceptible) – a survival tactic

  6. Microbiology of Bone and Joint infection- Foreign body • Decreased the minimal infecting dose of bacteria to initiate infection • - related to impaired phagocytosis at site if implant • Adherence. CoNS have virulence factors to facilitate rapid adherence to surface (adhesins) also electrostatic forces, hydrophobia • Bacterial cells adhere to adjacent ones form biofilm • Very difficult to remove or destroy biofilm once adherent • Culture of tissue will not culture organisms dormant under biofilm NB

  7. Prosthetic joint Infection • ~1% of all joint replacements become infected/year= 14,000 new infections/yr+ other pin/plate screw infections • early acute infection , fever acute hot joint • late chronic infection, longer duration of symptoms, no acute signs, pain may be present, usually discomfort, sinus, usually no fever. CRP variable

  8. Risk factors for PJI • Co-morbidityrheumatoid 2-6 x more likely cf osteoarthritisdiabetes mellitusany immunosuppression • Prior joint replacementPrimary revision 0.54% risk of infectionrepeat revision 4.2% risk of infection • Previous PJI in the joint • “Superficial” wound infection post op

  9. PJI Classification • Early <3months (29-45%). Skin flora • Late 3-24months (23-41%) • Delayed >24months (30-33%) • Early – typical acute signs, oedema, heat, erythema poor wound healing, haematoma , fever • Delayed – persisting joint pain, early loosening - few ‘typical’ signs of infection. x aseptic loosening • Late sudden onset symptoms or sub-acute infection after bacteraemia – which may have been sub-clinical

  10. Prosthetic joint Infection • Primary replacement<1% THR <2% TKR become clinically infected in 1st 2 years • Are susceptible to seeding (bacteraemia) lifelong • Latency up to 2 years for 1st peri-op infection • Under detected • Est incidence (hip and knees) 5.9/1000 prosthesis yrs in first 2 yrs post op 2.3/1000 prosthesis yrs in next 8 yrs post op

  11. PJI presentation • Early PJIMore systemic symptoms, wound usually looks infected NB the ‘wet wound’caused by virulent organisms eg MSSADifficult too treat conservatively unless caught very early • Delayed PJIlow grade infection or a partially treated early infection –suppressed by short antibiotic courseoften subtle signs and symptoms

  12. PJI presentation • Late infectionus by haematogenous seedingpain fever, signs of looseningNB patient with persistent  CRP after surgery • May follow evident infection eg pneumonia, cellulitis etc or after Staph aureus bacteramia which had no evident focus >33% of all Staph aureus bacteramia will result in PJI if prosthesis in situ.

  13. PJI presentation • signs are variable, loosening of joint often seen on X-ray (?aseptic) • stiff joint, ‘hasn’t felt quite right’ • may involve “low grade” pathogens e.g. Coagulase-negative staphylococci, often polymicrobial, • easy to dismiss cultured organisms as ‘contaminants’ of sample collection/handling if only 1 or 2 specimens sent • treatment depends on age, co-morbidity, bone stock, patient expectations • may require removal of the prosthesis

  14. Common organisms causing PJI ref Trampuz, 2005 swiss Med Wkly 135: 243-251

  15. Diagnosis of prosthetic joint infection • Diagnosis difficult • History, examination, ESR, CRP, X-rays, isotope scans, MC&S of joint aspirate. • Chronic infection, fewer clinical signs than acuteloosening may be aseptic • Bacteriological diagnosis very important • Gram stain of joint fluid – low sens. Culture better Atkins et al (1998) J Clin Micro 36: 2932

  16. Defining PJI • Pus at implant site intra- operatively, • neutrophils on histology at infection site • Presence of sinus tract communicating with joint • ≥2 specimens from joint tissues/specimens with identical organisms ie same genus, species and antibiogram.

  17. Diagnosis of prosthetic joint infection • indicators. WCC, CRP – non specific, CRP elevated til ~21 days post op. • Synovial fluid: WBC, neutrophil proportions • Histopathology: sens >80% spec>90%acute inflammation = >1 to >10 WBC pre high power field (averaged)but doesn’t give any clue re pathogen NB. *Only based on TKR infection data. Trampuz, 2004

  18. Diagnosis of prosthetic joint infection • MicrobiologySinus tracts - NO! poor correlation with organism unless Staph aureus • M<C&S tissues and fluid from 3-5+ site close to prosthesis and inflamed sites. Fresh instruments for each bite. • Tissue not swabs. • ?Stop antibiotics 2 weeks pre op if possible to improve yield • Direct Gram stain – culture onto agar for 48hrsindirect culture into enrichment broth – if turbid at 48 hours – culture onto agar

  19. Diagnosis of prosthetic joint infection. Novel methods • Sonication of removed prosthesisto remove adherent organisms from prosthesis surface • Higher sensitivity than MC&S • Particularly useful if antibiotics have been given within 14 days of operation (sens 75% vs 45% vs tissue culture) • But not in routine use • Molecular diagnosticsPCR, Broad range PCR, (±RFLP probe) • Useful, high PPV, high sens and specificity • – but slow, high labour intensity, contamination possible • No proven standard technique to assess these against

  20. PJI – what to do next? Patient expectations,co-morbidity Surgical feasibility • Surgical procedure • Timing • Antibiotic strategy Microbiological results, antibiotic options

  21. Treatment options for PJI • conservative,washout….debride, antibiotics retain implant “DAIR” • If recent diagnosis, joint stable , no sinus, organisms ‘amenable’ to conservative Rx • radical i.e. remove prosthesis1 stage2 stage • One stage – if little damage, susceptible organisms • Two stage – if more damage/disruption, organisms more difficult to treat

  22. Treatment options for PJI • lifelong suppression therapyif unfit for surgery.30-60% patients retain useful joint function • Suppression – if inoperable – or able to function if pain free will not be cured, will recur if outlive treatment ‘duration’ • ‘masterly inactivity’ (do nothing) if elderly, co-morbidities & current symptoms do not impact on quality of life • If no mobility to be regained, able to manage without cure & moderate analgesia

  23. Treatment of prosthetic joint infection • Treatment without removal. DAIR • Joint must be stable –not loose & soft tissues should be intact/minimal damage • Surgical drainage + >> 6 weeks antibiotics • may miss adherent bacteria if rely only on aspiration for diagnosis, bacteria attached to cement and prosthetic surfaces • Success rate ~ 20%, May be higher in: • early post-op cases, treatment initiated promptly e.g. 80% failure rate if debrided >2 days after symptoms presented • avirulent organisms i.e. not infected with Staphylococcus aureus or multi-resistant organisms

  24. Treatment of prosthetic joint infection • 1 stage replacement • Removal and replacement at the same operation (+ antibiotic loaded cement) • ~70-80 % success reported generally, but probably higher if cases carefully selected • Must have organisms which are ‘easy to treat’ (and sensitive to oral antibiotics with good bioavailability) • Allows earlier recovery, shorter admission time/theatre time, less damage to tissues

  25. Treatment of prosthetic joint infection • 2 stage removal • Removal and collection of multiple specimens followed by ~6 weeks or longer antibiotics (+/- cement spacer antibiotic-impregnated) then re-implantation once inflammation resolved (weeks-months) • 90- 95% success rate • May require plastic surgery, skin & muscle flaps • More surgery, GA, Admission duration for patients

  26. Antimicrobial therapy of PJI • Duration of IV antibiotics controversial! • Historically prolonged iv or iv-only therapy for duration • No RCTs though • Increasing reports of short course ivs, short course in entirety (iv + po) or reliance on antibiotics in cement without systemic antibioticssuccess rates 92-95% • AOC: We consider oral switch at 10-14days if: • Good response to iv Rx and surgery (CRP ↓, good healing) • oral options available acc to sensitivity testing with good bioavailability and able to kill adherent bacteria.

  27. Iv oral switch therapy • Variable opinions re acceptability of po antibiotics for PJI • Historical approach - extended duration iv antibiotics • No RCTS except for quinolone-rifampicin combinations • NBT  2 weeks iv then po if suitable agent availableBejon et al, UK 6 weeks iv before po switchHsieh et al Taiwan  1 week iv then stopWhittaker et al UK.  vanc x 2 weeks then stop ( + antibiotics in cement/spacer ). Bejon , P et al. J Antimicrob Chemother 2010: 65: 569-575 Hsieh,P-H et al . J Antimicrob Chemother 2009; 64: 392-397Whittaker et al J Bone joint Surg 2009: 91B: 44-51

  28. Factors in choosingan antimicrobial regime • Clinical trials • Relatively few - only RCTs using quinolones • ?Spectrum of activity* – may be multiple organisms • ?Potency* of antibiotics available • ?Bacteriostatic/bactericidal – *does it matter? • ?Bone penetration*Interpretation of results and studies difficult • ?Biofilm activity* • ? Oral bio-availability of intended po switch antibioticHow long is the course duration, 6 weeks? 6 months • How long to treat after re- implantation into ‘sterile’ joint space? • (*Find a keen medical microbiologist!)

  29. AOC approach to antibiotic treatment of PJI .Microbiological Outcome analysis • 2006-7, 1854 THR elective operations performed at AOC 1% indicated for a diagnosis of infected THR. • 25 patients identified who had a revision by 1 stage (n=19) or a 2-stage (n=6) for infected THR. • Follow up duration for all cases = 24-36 months. • 3 patients had died at time of follow up- without any further infective complications relating to their joint replacement. Darley et al . J Antimicrobial Chemotherapy 2011

  30. Interim analysis 2-year Outcome data. • 1-stage revision surgery. • 5/6 had between 7-20 days iv antibiotics followed by 6-26 weeks oral antibiotics. • 1 patient had 6 weeks oral antibiotics with no initial iv therapy. • Case notes are unavailable for 2 patients.2-stage revision surgery. • 15/19 were treated with between 12 -21 days iv antibiotics followed by oral antibiotics for 4-25 weeks. 2/19 patients were treated with iv antibiotics for the whole durationTwo other patients had 28 days iv antibiotics prior to oral switch

  31. Results.1 & 2-stage THR for infection. 2006-7 1-stage THR n=6 2-stage THR n=19

  32. THR infection AOC. • Summary =early iv –po switch is not detrimental to outcome • Patients prefer it. • Now looking to reduce iv duration to 7 days or less but should we be reducing all systemic antibiotics to <1 week and relying on antibiotic impregnated spacers/cement alone?? • NB not all antibiotics are compatible or stable in cement, some destroyed by heat treatment, some destabilise cement

  33. Prevention of post-operative infection • Asepsis in theatre • reducing contamination of the operative site • Prophylactic antibiotics • Careful handling of wound post op.Clean hands & gloves if wet.

  34. Classen et al. NEJM 1992, 326 (5): 281 • 2847 patients having elective clean or clean-contaminated operations

  35. Reducing contamination of the operative site • Main sources of contamination • Patient skin flora • Hands/skin of surgical team • Pre-existing infection • Airborne: skin / mucous membranes / clothing of patient or surgical team

  36. Reducing contamination of the operative site • Sterilisation of instruments • Disinfection of anaesthetic equipment • surgical team (min number) • Patient (should be sterile) • Order of cases (infected at end of list)

  37. Operating suite design • Separation from general traffic of hospital • Sequence of increasingly ‘clean’ zones from entrance to theatre • Movement between clean areas without passing through ‘dirty’ areas • Removal of waste without passing through ‘clean’ areas • Airflow from ‘ clean’ to ‘dirty’ – no backflow from corridors/sluice/anaesthetic room

  38. HTM 01-03 • the air supply to an operating room has 4 main functionsto control the temp & humidity of the spaceto assist removal of and dilute waste gasesto dilute airborne bacterial contaminationto control air movement within the suite such that transfer of airborne bacteria from less clean to cleaner areas is minimised

  39. UCV –plenum ventilation airflow

  40. UCV • 100airchanges/hr in theatre • 400airchanges/hr under hood • Final filter HEPA • Particles from skin fall down away from wound space • Noisy, evaporation+, costly to run (use setback facility) • Only evidence for use in joint replacement –not other implant surgery

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